Star delta starter working principle theory circuit

Star delta starter working principle theory circuit

Home Motor starter Star Delta Starter? One of them, popular and cheapest is a Direct online starter. But its use limited for smaller HP motor, to start higher rating 3 phase motors star-delta starter is used. Star-Delta starter is the simplest starting method for reducing the inrush starting current of Induction motor.

The reduction of the high motor current causes a reduction of the starting torque of the motor. Star-delta starting is therefore especially suitable for drives that are not loaded until after starting. The starting time is longer than with direct starting, which is especially apparent when driving larger inertial masses. To start a large motor we need a reduced voltage starter, to limit starting current.

Types of Star-Delta Starter 1 Manual star delta starter. Wye delta starter works in three states:. Star connected motor terminals current and voltage in star connection During the starting time of star delta starterMain contactor and star contactor remain in the close state and complete power circuit.

When motor attains sufficient speed of full speed i. M timer connected in circuit activated. Between switching from star to deltathe circuit becomes open and motor neither remain in star nor in delta state.

This state is called an open transition state. In delta connection state, phase voltage equal to line voltage. Hence full line voltage applied to motor winding and motor runs at its rated full speed.

These two contactors are the main contactor and delta contactor. Hence contactor rating is one-third of motor rated current. In star delta starter 3 contactors are used. Main contactor, star contactor, and delta contactor.

The current rating for contactor varies from 10 amps to several hundred amps. High current contactor is made from an alloy containing silver.

Star Delta Starter? Working principle,Theory, Circuit Diagram

Arcing during the switching operation of the contactor causes the contact to oxidize. However, silver oxide still a good conductor. Overload protection is provided along with the contactors to start the motor. A contactor is not used to interrupt a short circuit current, Unlike the circuit breaker used.

Contactor size varies from small to large for high current appliances. The majority of winding failure is because of overloading, Operation on unbalance supply voltage or single phasing due to phase loss which leads to excessive heating to degradation of winding insulation, due to this electrical motor required overload protection, to prevent damage from over-loading the motor, or to protect form sort circuit or internal winding fault of electric motor.

star delta starter working principle theory circuit

Fuse unit is used to protect the motor from over current or short circuit conditions. The main purpose of the fuse is to protect the motor and is composed of an alloy which has a low melting point. A strip of a fuse is placed in series with the motor circuit. Its main function is to break the current flow after a fault is detected.

On Other hand a fuse, which operates once and then must be replaced, a circuit breaker can be reset to begin normal operation.Premium Membership.

Study specialized technical articles, electrical guides, and papers. Most induction motors are started directly on line, but when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges. To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed.

Two methods used for reduction of starting voltage are: Star delta starting and Auto transformer starting. This is the reduced voltage starting method.

Star Delta Starter Explained - Working Principle

Voltage reduction during star-delta starting is achieved by physically reconfiguring the motor windings as illustrated in the figure below.

During starting the motor windings are connected in star configuration and this reduces the voltage across each winding 3. This also reduces the torque by a factor of three. After a period of time the winding are reconfigured as delta and the motor runs normally. They are used in an attempt to reduce the start current applied to the motor during start as a means of reducing the disturbances and interference on the electrical supply.

The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only. There are two contactors that are close during run, often referred to as the main contractor and the delta contactor.

star delta starter working principle theory circuit

The third contactor is the star contactor and that only carries star current while the motor is connected in star. The main circuit breaker serves as the main power supply switch that supplies electricity to the power circuit. In operation, the Main Contactor KM3 and the Star Contactor KM1 are closed initially, and then after a period of time, the star contactor is opened, and then the delta contactor KM2 is closed. The control of the contactors is by the timer K1T built into the starter.

The Star and Delta are electrically interlocked and preferably mechanically interlocked as well. The star contactor serves to initially short the secondary terminal of the motor U2, V2, W2 for the start sequence during the initial run of the motor from standstill.

This provides one third of DOL current to the motor, thus reducing the high inrush current inherent with large capacity motors at startup.

Controlling the interchanging star connection and delta connection of an AC induction motor is achieved by means of a star delta or wye delta control circuit.

The control circuit consists of push button switches, auxiliary contacts and a timer. This sequence happens in a friction of time. After pushing the ON push button switch, the auxiliary contact of the main contactor coil 2 which is connected in parallel across the ON push button will become NO to NC, thereby providing a latch to hold the main contactor coil activated which eventually maintains the control circuit active even after releasing the ON push button switch.

Now Motor terminal connection change from star to delta connection. Thus, the delta contactor coil cannot be active when the star contactor coil is active, and similarly, the star contactor coil cannot also be active while the delta contactor coil is active. The control circuit above also provides two interrupting contacts to shutdown the motor. The OFF push button switch break the control circuit and the motor when necessary. The thermal overload contact is a protective device which automatically opens the STOP Control circuit in case when motor overload current is detected by the thermal overload relay, this is to prevent burning of the motor in case of excessive load beyond the rated capacity of the motor is detected by the thermal overload relay.

At some point during starting it is necessary to change from a star connected winding to a delta connected winding. Power and control circuits can be arranged to this in one of two ways — open transition or closed transition. Discuss mention above is called open transition switching because there is an open state between the star state and the delta state.

In open transition the power is disconnected from the motor while the winding are reconfigured via external switching. When a motor is driven by the supply, either at full speed or at part speed, there is a rotating magnetic field in the stator. This field is rotating at line frequency. The flux from the stator field induces a current in the rotor and this in turn results in a rotor magnetic field. When the motor is disconnected from the supply open transition there is a spinning rotor within the stator and the rotor has a magnetic field.

Due to the low impedance of the rotor circuit, the time constant is quite long and the action of the spinning rotor field within the stator is that of a generator which generates voltage at a frequency determined by the speed of the rotor. Open transition starting is the easiest to implement in terms or cost and circuitry and if the timing of the changeover is good, this method can work well.The Star Delta Starter is a very common type of starter and is used extensively as compared to the other type of starting methods of the induction motor.

A star delta is used for a cage motor designed to run normally on the delta connected stator winding. The connection of a three-phase induction motor with a star delta starter is shown in the figure below. When the motor picks up the speed, about 80 percent of its rated speed, the switch S is immediately put into the RUN position.

The delta connection of the stator winding in shown in the figure below. Firstly, the stator winding is connected in star and then in Delta so that the starting line current of the motor is reduced to one-third as compared to the starting current with the windings connected in delta.

Here V L is the line voltage. Since the developed torque is proportional to the square of the voltage applied to an induction motor. Star delta starter reduces the starting torque to one-third that is obtained by direct delta starting. Thus, with star delta starter, the starting current from the main supply is one-third of that with direct switching in the delta. Hence, with star delta starting, the starting torque is reduced to one-third of the starting torque obtained with the direct switching in the delta.

Hence, the equation 4 shown above gives the starting torque of an induction motor in the star delta starting method. Thank you so much Excellent information in a simple language It is very helpful to me…. Once again thank you……. Sir in star delta starter timer sec is 10 sec. But the contactor changing star to delta immediately why?

Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Circuit Globe All about Electrical and Electronics. Electronic Instrumentation. It is very easy to understand …. Prsntsation than earlier of any one. Thank you so much for sharing such a simple yet detailed explanation.

Really easy to understand about starting of induction motor by star-delta starter, thank you. The way you explained was awesome, quite easy and understandable.

I love this article. It is very good for me. Thank you. Leave a Reply Cancel reply Your email address will not be published.Induction motor is the most frequently used motor for industrial as well as domestic applications.

Ac motor is become most popular because of its simple and robust construction, low maintenance and can be suitable for any working condition. Due to its numerous applications, the induction motor needs some starting arrangements to start softly and safely.

Various starting methods are used to start induction motors like star delta starterDOL starterauto transformer startersoft starterand VFD. In this article we are going to discuss Soft starter for three phase induction motor, soft starter circuit, soft starter working, application, advantages, block, power, control diagram, working principle, uses. Soft Starter is another form of reduced voltage starter use for starting 3 phase induction motor.

Soft Starter also called a Solid-State controller. Soft Starter does not change frequency as VFD. Instead it Ramp up voltage level applied to motor from initial value to full voltage. Initially applied voltage is low which is only to overcome gear wheels or stretching driving belts etc. Gradually voltage increase, the torque also increases and motor start to accelerate.

Advantages of soft starter starting methods are the possibility to adjust torque as per exact need. By the use of soft starter starting current reduced, this helps to protect the motor from taking high starting current and also prevents a huge voltage drop in supply.

Soft Starter also provides a soft stop as a start. Hence it can be suitable where soft stopping is required like a conveyor belt, water pumps. Soft Starter contains only a few main components thyristor to regulate the voltage to the motor. In addition to this heat sink and fan for dissipate the heat to the environment. Depending on the model of the soft starterit can be equipped with a built-in electronic overload relay EOL eliminating the need for an external relay.

Soft Starter contains the number of anti parallels connected thyristor. Each phase has a pair of the thyristor. A thyristor is semiconductor devices which are normally isolation but applying firing signal to gate, they start conducting and allowing pass current and voltage through it.

At a time of start to perform soft starting firing signal is sent to thyristors so that only the last part of each half period of sinusoidal voltage wave is passed through it. And after the start, firing signal send to earlier and earlier, to allow bigger and bigger part of voltage wave to pass through thyristor. At first, the full voltage is allowed to pass through the thyristors and as the stop initiate, the firing signal is sent later and later allowing less and less of the voltage to pass through until the end voltage is reached.

Then no more voltage is applied to the motor and the motor stops. Start: Thyristor allows part of voltage through it initially and after increase accordingly ramp-up time set for starting. Stop: Thyristor is in full conducting mode when soft stop begain, voltage decreases as ramp time set for the stop. Soft Starter connection Diagram. This way of connecting a soft starter is most common. All three phases are connected in series with the main contactor, overload relay and soft starter following motor.Start Delta Starter is a scheme for motor starting to reduce the inrush current during starting of the motor.

This method of starting is quite popular for Delta connected Squirrel Cage induction motor. In this method, the motor is first started as a star connected motor and as soon as the motor reaches near to or rated speed, it is run as Delta connected motor. In this post, we will be discussing the requirement, working principle and disadvantage of Star Delta Starter. As we know that when a 3 phase induction motor is started at its rated voltage, it draws high inrush current whose magnitude is around 5 to 7 times of the rated motor current.

This means, if the rated current of a motor is 20 A then during starting it will take around to A.

This high value of starting current may result in considerable voltage dip of the supply line feeding the motor. Due to this voltage dip, the other equipment connected to the supply may get effected.

In order to limit this starting current to some reasonable value, some methods are adopted to start three phase induction motor. Star Delta Starter is one among the various starting methods. As discussed earlier, star delta starter automatically changes the motor winding configuration from STAR during starting to DELTA when the motor reaches its rated speed.

What is Soft Starter,Working Principle,diagram,advantages

This itself means that all the six winding terminal of motor must be taken out and connected to the starter. This nomenclature can easily be seen in the motor terminal box. Schematic diagram of star delta starter is shown below. Let us now consider two cases to better understand the functioning of this starter.

Under this assumed condition, motor winding terminals A2, B2 and C2 are shorted by the switch as can be seen in the schematic diagram. You might think what we are achieving by making motor STAR connected during starting? The straight forward answer is to limit the magnitude of starting current. But ,how? If V L be the line voltage and Z be the standstill per phase leakage impedance, then per phase starting current I 1 flowing through the motor will be given as below.

Since motor is STAR connected, hence phase and line currents will be same. Therefore line current. In this case, the per phase motor starting current I 2 will be. Line current in DOL starting. This is the reason we go for star delta starter.

A control scheme is implanted to make the process of automatic and smooth. The major disadvantage of star delta starter is reduced starting torque.A Dual starter connects the motor terminals directly to the power supply.

Hence, the motor is subjected to the full voltage of the power supply. Consequently, high starting current flows through the motor. This type of starting is suitable for small motors below 5 hp 3. Reduced-voltage starters are employed with motors above 5 hp. Although Dual motor starters are available for motors less than kW on V and for motors less than 1 MW on 6.

Supply reliability and reserve power generation dictates the use of reduced voltage or not to reduce the starting current of an induction motor, the voltage across the motor need to be reduced. This can be done by. In dual starter the motor is directly fed from the line and in star delta starter then motor is started initially from star and later during running from delta. L start. They are used in an attempt to reduce the start current applied to the motor during start as a means of reducing the disturbances and interference on the electrical supply.

The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only.

star delta starter working principle theory circuit

There are two contactors that are close during run, often referred to as the main contactor and the delta contactor. The third contactor is the star contactor and that only carries star current while the motor is connected in star. The current in star is one third of the current in delta, so this contactor can be AC3 rated at one third of the motor rating.

In operation, the Main Contactor KM3 and the Star Contactor KM1 are closed initially, and then after a period of time, the star contactor is opened, and then the delta contactor KM2 is closed. The control of the contactors is by the timer K1T built into the starter. The Star and Delta are electrically interlocked and preferably mechanically interlocked as well. This type of operation is called open transition switching because there is an open state between the star state and the delta state.

Thanks for your wonderful site sir. It will be very useful. But,please provide the working principle of all the Equipments like Instruments,Electrical,Electronics,etc in automation. It will be more easy to understand practically. Expecting your work asap. Save my name, email, and website in this browser for the next time I comment. This website uses cookies to improve your experience.

We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More. Primary Menu Inst Tools. Search for: Search. Previous Article. Next Article. Selecting the Best Inductive or Capacitive Sensor. Related Articles. S Bharadwaj Reddy July 11, July 11, XYZ November 10, at am Thanks for your wonderful site sir. Leave a Comment Cancel Reply Save my name, email, and website in this browser for the next time I comment.Most induction motors are started directly on linebut when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges.

To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed. Two methods are used for reduction of starting voltage are star delta starting and auto transformer stating.

Would you pls help me by giving some information about SLD. Your email address will not be published. Skip to content Most induction motors are started directly on linebut when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges.

star delta starter working principle theory circuit

Voltage reduction during star-delta starting is achieved by physically reconfiguring the motor windings as illustrated in the figure below. During starting the motor windings are connected in star configuration and this reduces the voltage across each winding 3.

This also reduces the torque by a factor of three. After a period of time the winding are reconfigured as delta and the motor runs normally. They are used in an attempt to reduce the start current applied to the motor during start as a means of reducing the disturbances and interference on the electrical supply.

Traditionally in many supply regions, there has been a requirement to fit a reduced voltage starter on all motors greater than 5HP 4KW. The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only. There are two contactors that are close during run, often referred to as the main contractor and the delta contactor. The third contactor is the star contactor and that only carries star current while the motor is connected in star.

Power Circuit of Star Delta Starter: The main circuit breaker serves as the main power supply switch that supplies electricity to the power circuit. In operation, the Main Contactor KM3 and the Star Contactor KM1 are closed initially, and then after a period of time, the star contactor is opened, and then the delta contactor KM2 is closed.

The control of the contactors is by the timer K1T built into the starter. The Star and Delta are electrically interlocked and preferably mechanically interlocked as well. In effect, there are four states: The star contactor serves to initially short the secondary terminal of the motor U2, V2, W2 for the start sequence during the initial run of the motor from standstill. This provides one third of DOL current to the motor, thus reducing the high inrush current inherent with large capacity motors at startup.

Controlling the interchanging star connection and delta connection of an AC induction motor is achieved by means of a star delta or wye delta control circuit. The control circuit consists of push button switches, auxiliary contacts and a timer. This sequence happens in a friction of time. After pushing the ON push button switch, the auxiliary contact of the main contactor coil 2 which is connected in parallel across the ON push button will become NO to NC, thereby providing a latch to hold the main contactor coil activated which eventually maintains the control circuit active even after releasing the ON push button switch.

Now Motor terminal connection change from star to delta connection. Thus, the delta contactor coil cannot be active when the star contactor coil is active, and similarly, the star contactor coil cannot also be active while the delta contactor coil is active. The control circuit above also provides two interrupting contacts to shutdown the motor.

The OFF push button switch break the control circuit and the motor when necessary. The thermal overload contact is a protective device which automatically opens the STOP Control circuit in case when motor overload current is detected by the thermal overload relay, this is to prevent burning of the motor in case of excessive load beyond the rated capacity of the motor is detected by the thermal overload relay.

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